Method for making shaped carbides of cohesively intertangled single fibers

ABSTRACT

Cellulosic single fibers such as cotton is prepared without any resins or pitches to a mass or bulk such as a lap which is self-shaped and retains its form by a force of cohesive intertanglement of fibers. The mass as prepared is heated for carbonization or graphitization, if desired, to obtain unique shaped carbides of porous and stable structures in which the cohesion of fibers is made more dense on account of the total shrinkage of the mass by carbonization.

This application is a divisional of Ser. No. 08/967,237 filed Nov. 5,1997 now U.S. Pat. No. 6,013,207 which is continuation of Ser. No.08/534,207 filed Sep. 26, 1995, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a method for making shaped or figured carbideswhich are consisted of a self-figurable flock, mass, or bulk of singlefibers. More specifically, it relates to a method for making shaped orbulked carbides, in which a flock of cellulosic single fibers which hasbeen prepared by binding the fibers by means of their intertwiningproperties, is heated for carbonization, whereby it can have a strongtissue afforded with high carbonic characteristics and can presentporously shaped fibrous structures.

Heretofore, carbonaceous or carbon substances which are prepared fromorganic matters (hereinafter called generally as carbides) are employedin various industrial applications in accordance with characteristicsthey have, viz., adsorption, electrical, adiabatic, thermal resistant,corrosion resistant, mechanical, and other characteristics. In either ofsuch applications, carbides have to be shaped to a form appropriate to apurpose of applications. There are known, for example, powdery,granular, and crashed carbides. And, fibrous carbides which arepopularly called as carbon fibers, are available in long or lintfibrous, short or fuzz fibrous, woven, sheet or mat-like, and braidedforms. In order to improve their mechanical characteristics, they areoften prepared to composite materials by mixing and treating them withother materials such as resins and pitches.

In any case, in order to shape them to a form appropriate to a purposeof applications, they must be subjected to a secondary treatment processin addition to preceding carbonization process. More particularly, incase of obtaining powdery carbides, carbides have to be pulverized andsieved after carbonization, and in case of utilizing long fibrouscarbides as flakes, they have to be subjected to a chopping process.And, in case of utilizing long fibrous carbides as woven or braidedforms, they have to be subjected, after carbonization, to a weaving orbraiding process. In such secondary processes, there are muchdifficulties to prepare them to a desired form. That is, as carbonfibers have inherently a poor elongation and lack in a bending force,they can tolerate to be woven only into comparatively flat stuff havinglittle bending but not into thick and porous structures.

When short fibrous carbides which have been obtained by chopping asmentioned above, are shaped into sheets or mats by a paper-makingprocess in which an adhesive binder is added as an auxiliary agent tothe carbides so that they can be integrally shaped, they can produceonly those which are flat and thin. There is observed anotherdisadvantage that such auxiliary agent tends to adversely affectcharacteristics carbides properly have.

As described above, secondary processing to be adopted for shapingcarbides into forms appropriate to their applications, are complex, andin certain cases, it adversely affects characteristics the carbides haveand increases a production cost fruitlessly.

BRIEF SUMMARY OF THE INVENTION

Accordingly, this invention is to provide a method for making carbideswhich are self-shaped to have stable porous fibrous structures suitablefor fully demonstrating the characteristics the carbides have andaccordingly suitable to various applications, whereby such carbides aremade by a simple method, at a low production cost, and without problemsinvolved in the conventional production and employment of carbides.

More particularly, in the method for making shaped carbides ofintertangled single fibers in accordance with this invention, it ischaracterized that porous structured raw materials which are made from afigurable intertangled mass of cellulosic single fibers, are heated, asthey are shaped, in an non-oxidation atmosphere for carbonization sothat entanglement among the single fibers are stiffened on account ofshrinkages of the raw materials when they are subjected to thecarbonization, exhibiting stable porously shaped fibrous structures. Itis accordingly preferable that in respect of structural features, thecellulosic single fibers employed in this invention are those twisted,threaded, waved, curled, or frizzled, that in respect of functionalfeatures, they can get entangled easily, and that in respect of physicalfeatures, their outer surface areas are remarkably large. It is alsopreferable in this invention that fibrous raw materials which are madefrom a mass of entangled single fibers as mentioned above, are selectedfrom a group consisted of those loose fibers, laps, slivers, and rovingswhich are light in weight and have porous structures.

DETAILED DESCRIPTION OF THE INVENTION

This invention is described below more in detail.

It is the first features of this invention that since the raw materialsare consisted of cellulosic single fibers which are slender, haveextremely large outer surface areas, and can easily get entangled eachother, they can readily be shaped to a desired form of soft and porousmass of single fibers without employment of any binding agent. When suchfigurable raw materials are heated for carbonization as they areself-shaped, it is noticed that while the single fibers which constitutea mass of the raw materials, are converted to carbides with the progressof carbonizing reactions, they are shrinked as a whole at a constantdecrement rate, keeping, continuously till the end of heat treatment,the form to which they have been shaped. This phenomena support workingprinciples of this invention that single fibers can produce a carbonizedlight and porous mass, and its structures become stronger bycarbonization.

While it is known that a mass of raw materials generally loses itstenacity and tends to get hardened when carbonized, an apparent hardnessof the mass changes little in this invention, because only slendersingle fibers of a low denier constitute the mass in this invention.This is comparable to the fact that when a sheet of hard glass isconverted to glass fibers, they exhibit softness.

For example, compared to those materials which are conventionally usedfor carbonization, such as coconut husks and sawdusts which are oftenemployed for the manufacture of an activated carbon, single fibersemployed as raw materials in this invention are extremely slender. Morein concrete, a fiber width of those cellulosic single fibers which areemployable in this invention, is as narrow as 0.01-0.08 mm, and theirsurface areas are several hundred times of those of the above-mentionedtwo kinds of raw materials.

Accordingly, it is the second features of this invention that carbidesof a mass consisted of single fibers are extremely highly reactive, andconsequently that certainly in the carbonization process and also in aprocess for reactivating the carbides which is conducted in case ofneed, their reaction speed is high and reaction proceeds evenlythroughout the mass. This is one of the advantages attained by thisinvention.

The raw materials and carbonization treatment employed in thisinvention, and physical, electrical, and other properties of thecarbides obtained by this invention are explained below further indetail.

The principal component of single fibers employed in this invention asraw materials, is cellulose, and their fiber width is preferably about0.01-0.08 mm. They may be natural fibers as well as those syntheticfibers which are consisted of regenerated cellulose, such as fibers ofcotton, flax, hemp, jute, ramie, paper mulberry, Edgeworthia chrysantha,bamboo sugarcane, rayon, and others.

In case of cotton fibers, for example, it is not necessary to improvetheir intertwining properties because they are well provided withnatural twists which are spirally turned, while it is preferable totreat fibers preliminarily to carbonization, so that they will be givensynthetically with waves or curls, if they are not provided with naturaltwists and so on. For example, such waves or curls may be given tofibers by passing them between a pair of mold rollers which are heatedand face each other for pressing the fibers therebetween.

Those single fibers which are provided with intertwining features orcohesive property, are prepared to a shaped porous mass by machinesconventionally utilized in spinning processes. That is, in order toobtain loose fibers, fibrous raw materials are put into a boll breaker,whereby those in a compact group are opened. When they are subjected toa cotton gin, laps are obtained. Slivers are obtainable when the lapsare further treated by a carding machine. Rovings are obtained bytreating slivers with a flyer frame, while giving them mild twists.

Baking carbonization of those fibrous materials is made generally byheating them to more than 300° C. in a non-oxidation atmosphere forabout 6 hours, although such heating conditions may be adjusted properlyin view of properties to be afforded to the materials when carbonized.As a carbonization degree and change in shape of the materials vary inaccordance with the heating conditions, they shall be adjusted to fitthe purpose.

General, physical, and electrical properties of those shaped carbideswhich are obtainable in this invention, are as follows.

Although carbides have been used for a long time as functionalcomponents or parts in various fields, and their applications in today'smodern technologies are remarkable, those which are used today remain asthey were, and they are mostly powdery, granular, or crushed, exceptcarbon fibers which have been recently developed and employed limitedlyin certain industrial fields.

In order to meet them to their applications, it is necessary asdescribed above to process them to compounds by adding other elements tothem. This enlarges their application fields, while it inducesdisadvantageous aspects too, such as complex manufacturing steps andadmixture of foreign objects.

Characteristic physical properties of the shaped carbides made inaccordance with this invention are enumerated in the following.

When they are macroscopically observed, they are soft, light in weight,and porous, and their bulk density is about 0.02-0.025 g/cm³. Theirsoftness is comparable to that of their raw materials (mass of singlefibers which have not been carbonized). As they are supple for one ofcarbides, it is far easier than in the case of carbon fiber compounds tomatch them with desired applications. The weight of them which cantransform quite freely, is reduced to about 33-45% of their originalweight before carbonization. While their porosity is reduced also byabout 20-30% of the raw material, their air and liquid permeability isas low as about ⅕-{fraction (1/15)} of conventional powdery and gramlarcarbides and carbon fiber webs.

When they are microscopically observed, it is noticed that a fiber widthof carbonized single fibers is reduced by about 30-40% of that of rawmaterials, and they become more slender. As their adsorption propertiesare accordingly improved because that their surface area per an unitweight increases, the adsorption speed and saturated amount ofadsorption are remarkably large, compared to those of conventionalcarbides.

Electrical properties of the shaped carbides made in accordance withthis invention are explained below. Electrical properties of carbidesare basically dependent upon superiority or inferiority of electricalconductivities they have. Particularly in the shaped carbides of thisinvention, as their conductive paths are formed by direct contacts amongtheir carbonaceous substances, electrical properties are largelyinfluenced in proportion to their densities. Since the shaped carbidesof this invention is high in density, and their cohesion and contactdensities are large, they exhibit extremely good efficiencies when theyare applied for the prevention of electric charge, shielding ofelectromagnetic waves, and surface heat generation, and as variouselectrodes, electrical double condensers, and so on.

It shall be noted also that their thermal resistant property isexcellent on account of the porosity they have, and that their lightnessin weight is advantageous in designing machinery incorporating them. Asthey are porous as well as soft, they can get readily fit machinery orhousings when they are used as shielding or packing materials. Forexample, the carbides of this invention are employable for theadsorption or filtration of air or gas, simply by packing them into atubular housing or by mounting them over the housing. Such features thatthey can be conversed freely to various forms, are unprecedented andextremely advantageous in their applications.

Examples of this invention are given below.

EXAMPLE 1.

As a starting material, there were employed cotton fibers which wereproduced in United Sates, and had a fiber width of 0.02-0.05 mm, lengthof 15.0-50.0 mm, and number of natural twists of 140-240 turns/2.5 cm.The fibers were treated by a boll breaker and a cotton gin for obtaininga lap. This lap was cut to have a width of 14 cm, and wound up looselyaround a tubular iron core.

This lap loaded about the core was mounted in a carbonization furnacewith a non-oxidation atmosphere. The temperature within the furnacecontained with the lap was gradually raised until it reached 600° C. Atsaid temperature, the lap was heated further for 3 hours for acarbonization baking treatment.

The carbides thus obtained had a shape in proportion to the one theoriginal cotton lap had, while their tissues become more dense, anddimensions were reduced 29% in width and 35% in thickness compared tothe original cotton lap. Their weight was reduced 63%, and bulk densitywas 0.023.

Tensile strength of the shaped carbides thus made, was measured as shownin the following Table 1.

TABLE 1 Original lap of 3.87 cm in width Carbonized lap of (Note-1) 3.00cm in width Apparent tensile Laterally 33.0 48.6 strength (g′)Vertically 95.6 85.6 (Note-2) (Note-1) The width of 3.87 cm of theoriginal cotton lap became 3.00 mm, being shrunken by carbonization.(Note-2) Numerical values of the tensile strength shown in the Table arenot those when they were actually cut off, but g′ values when fibrouslayers were released from their cohesive intertanglement, and presentedbroken appearances, being dangled.

From the results shown in the above Table 1, it is observed thatalthough the actual tensile strength of the lap carbides should had beenlowered, their apparent tensile strength did not differ much from thatof the original lap on account of the cohesive intertanglement offibers, and it is presumed that the lateral strength was ratherincreased on account of that the intertanglement was densed andreinforced by carborization.

The original lap and the corresponding lap carbides obtained in thisExample 1 were immersed and boiled in water for determing their physicalstability. The results are given in the following Table 2.

TABLE 2 Test of stability (immersed in 100° C. water for 30 minutes)Original lap Carbonized lap before after im- before after im- immersionmersion test immersion mersion test Lateral 10.0 12.0-13.0 10.0 9.0-10.0 dimension (cm) Vertical 5.0 6.0-7.5 5.0 4.8 dimension (cm)

From the result shown in the above Table 2, it is observed that thedimensions of the original row lap varied much both laterally andvertically, particularly largely in its vertical direction because thata cohesive intertwining force among the fibers in the vertical directionwas comparatively weak, while the lap carbides were not deformed muchand their surface tissues were uniform and smooth even after theimmersion test was conducted.

EXAMPLE 2.

Cotton same to the one used in Example 1 as a raw material, was evenlyopened by a boll breaker to obtain a loose fiber (this invention sampleA).

Viscose rayon filaments of 1.5 denier which had been processed to bewaved by the employment of a pair of pressing mold rollers heated to400° C. at their surfaces, were cut to 2.5 cm and thoroughly opened toobtain a sample (this invention sample B).

As comparative samples, there were prepared a No. 8 cotton canvas(comparison sample C), a cotton rope of 4 mm in diameter (comparisonsample D), and a braid of 2.5 mm in diameter made from theabove-mentioned viscose rayon filaments (comparison sample E).

They were mounted in a carbonization furnace, and a temperature of thefurnace was raised gradually while the air was shut out from thefurnace, until it reached 840° C. in 2.5 hours. At 840° C., they arefurther heated for 3.5 hours to complete their carbonization.

This invention samples Aand Bthus heat-treated were carbonized loosefibers in which the fibers were densely intertangled each other topresent porous structure.

After all of the samples thus treated (this invention samples A and B,and comparison samples C, D, and E) were kept in the furnace at 800° C.and subjected to a steam activation treatment for 40 minutes, they werecooled in the furnace to a room temperature and then taken out from thefurnace.

In order to compare their reactivities, Methylene Blue adsorption testwas made to obtain the results shown in the following Table 3.

TABLE 3 Adsorption Properties Adsorption speed Adsorption saturation(Note-3) amount (Note-4) This invention  4 0.045 sample A This invention4-5 0.050 sample B Comparison 110 — sample C Comparison  98 — sample DComparison 370 — sample E (Note-3) Time (minutes) required for thesample carbides of 1 g′ (absolutely dried) to completely adsorb 0.001 gof Methylene Blue. (Note-4) Maximum amount (g′) the sample carbides of 1g′ (absolutely dried) had adsorbed.

As the results in the Table 3 indicate, adsorption efficiencies ofcarbides do not depend on materials of which they are composed, butdepend on structures or tissues they have. The self-shaped carbides madein accordance with this invention have accordingly a high surfacereactivity which can not be expected to conventional carbides.

As described above, by the method of this invention, those shapedcarbides, processing and reactivity of which are easy and excellent,which are light in weight and have soft porous fiber structuresappropriate to various applications, and which have also stable tissuessuited to present high carbon characteristics, can be manufactured by anextremely simple manner and at a low production cost.

While the single fibers were heat-treated to carbonization in the aboveexamples, they may be heated to graphitization. This is also within thescope of this invention.

What is claimed is:
 1. A method for using a shaped carbonaceous materialcomprising the steps of: a) providing a shaped carbonaceous material,the shaped carbonaceous material made by forming a plurality ofbinder-free, single fibers into a shaped self-supporting mass of singlefibers wherein the single fibers primarily consist of cellulose fibersand each configuration of which is non-linear s as to be entangled withone another, the shaped self-supporting mass of single fibers isprepared as loose fibers, laps, slivers, or rovings and the shapedself-supporting mass of single fibers is not needle-punched,sufficiently heating the shaped self-supporting mass of single fiberswhich is binder-free and not needle-punched, to cause at least one ofcarbonization and graphitization of the single fibers whereby the singlefibers are thoroughly entangled with one another and the shapedself-supporting mass is made stable, the shaped carbonaceous materialhaving a bulk density of about 0.025 g/cm³ or less and is soft, lightand porous; b) positioning the shaped carbonaceous material for thepurpose of making it to be adjacent a fluid to be adsorbed; and c)allowing the fluid to contact the shaped carbonaceous materialsufficient to permit adsorption of the same.
 2. The method according toclaim 1, and wherein the bulk density is about 0.02 g/cm³ or more. 3.The method according to claim 1, and wherein each configuration of thecellulosic single fibers is non-linear due to at least one of twisted,waved and curled shapes.
 4. The method according to claim 1, and whereinthe cellulosic single fibers are each within the range of about 0.01 toabout 0.08 mm in width.
 5. The method according to claim 1, and whereinthe mass of single fibers is heated for more than about 3 hours at atemperature of higher than about 300° C.
 6. The method according toclaim 1, and wherein heating the shaped self-supporting mass of singlefibers sufficient to reduces its weight by about 33-45%, its porosity byabout 20-30%, and the width of fiber thereof by about 30-40%.
 7. Themethod of claim 1, and wherein the fluid is a gas.
 8. The method ofclaim 1, and further including the step of: a) packing the shapedcarbonaceous material into a housing through which the fluid to beadsorbed will pass.